1. Field of the Invention
This invention relates to new copolymers of olefinically unsaturated monomers containing primary amino groups and to a process for the production of these copolymers.
2. Description of the Prior Art
Copolymers of olefinically unsaturated monomers containing primary amino groups are known. EP-A-0 101 962 for example describes polymers containing primary amino groups, a process for their production and their use. These aminofunctional polymers are produced by reacting a hydroxyl group-containing ester of an .alpha.,.beta.-olefinically unsaturated mono- or dicarboxylic acid and an dihydric alcohol (such as hydroxyethyl acrylate) with a diisocyanate at an equivalent ratio of NCO to OH groups of greater than 1:1 in a first step. This produces an .alpha.,.beta.-olefinically unsaturated mono- or diisocyanate which, in a second step, is subjected to radical polymerization with other monomers to form an isocyanate-functional copolymer. In a third step, the isocyanate groups of the copolymer are converted into ammonium salts by reaction with excess mineral acid (concentrated HCl) and water with elimination of CO.sub.2 and, in a fourth step, the ammonium salts are neutralized by the addition of a base (methanolic KOH). Copolymers containing free amino groups are obtained.
The disadvantage of this process is that the isocyanate-functional monomers obtained in the first step are not completely uniform 1:1-adducts, which can result in crosslinked products in the second step (the polymerization step) unless an elaborate purification process has been carried out beforehand. Another disadvantage lies in the very involved production of the amino-functional polymers in a total of four reaction steps. Another disadvantage of this known process is that because of the severe hydrolysis and neutralization conditions (concentrated HCl, KOH), not only are the isocyanate groups susceptible to hydrolysis, the (meth)acrylate units are also susceptible to undergoing partial hydrolysis, resulting in degradation of the polymer.
EP-A-0 179 954 describes two-component coating systems based on amino-functional and epoxy-functional polyacrylate systems. In this case, the amino-functional polymer is produced by preparing a carboxyl-functional copolymer in a first step using (meth)acrylic acid as the functional monomer together with other monomers. To introduce the amino groups, this copolymer is reacted with propylene imine in a ring-opening reaction accompanied by the formation of primary amino groups. A serious disadvantage of this process is that propylene imine, like ethylene imine, is an extremely dangerous substance which has been proven to be carcinogenic in animal tests.
U.S. Pat. Nos. 4,659,770 and 4,699,936 describe amino-functional copolymers which are used as binder components in two-component paints. They are produced by initially synthesizing aminofunctional (meth)acrylate monomers by the reaction of alkane diol di(meth)acrylates (such as hexane diol diacrylate) with diamines in quantitative ratios which form 1:1 adducts containing both free amino groups and also unsaturated (meth)acrylate groups. These amino-functional monomers are then copolymerized with other unsaturated monomers to obtain the amino-functional copolymers. The disadvantage of this process is that difficulties are involved in the production and processing of the amino-functional monomers. Thus, relatively high molecular weight oligomers may also be formed in addition to the desired 1:1 adducts. These oligomers promote gelation by acting as unsaturated crosslinking agents in the subsequent copolymerization process. Another disadvantage is that monomers containing both an unsaturated, activated (meth)acrylate double bond and a free, primary amino group are not stable in storage because both groups enter into an addition reaction with one another, even at room temperature. This addition reaction takes place considerably more quickly at elevated temperatures, for example, at the stated reaction temperatures of 90.degree. to 100.degree. C., so that unwanted secondary reactions resulting in gelled products can take place. Another particular disadvantage of this process is that dark-colored products are always formed when radical copolymerization processes initiated by organic peroxides are conducted in the presence of amino groups. Because of their color, these products are totally unsuitable, for example, for use as binders in high-quality paints.
An object of the present invention is to provide new copolymers containing primary amino groups which do not suffer from the above-mentioned disadvantages of the prior art. It is a further object of the present invention to provide copolymers containing amino groups which may be readily obtained without complications from safe, inexpensive and generally available raw materials and which are readily soluble in common organic solvents to form colorless or only faintly colored polymer solutions.
These objects may be achieved in accordance with the copolymers of the present invention as described in detail hereinafter.